1. Field of the Invention
The present invention relates to a three dimensional audio reproduction apparatus, and more particularly, to an audio reproduction apparatus and method for a loudspeaker using virtual sound images whose positions can be adjusted, the apparatus and method used in portable/personal multi-channel audio players, portable/personal digital audio broadcasting receivers, multimedia personal computers, HD television, audio/video home theatre systems and video conferencing.
2. Description of the Related Art
Conventionally, when an auditor intends to adjust the positions of loudspeakers or the space between the loudspeakers according to the auditor's taste, the auditor must directly move loudspeaker units to change their positions and angles. However, as technology develops, a process can be performed such that sound images are produced at the positions of virtual loudspeakers existing in a virtual space.
When changing the position of a virtual sound image using a conventional, three dimensional audio reproduction method, all the coefficients of a transfer function corresponding to the position must be provided so that a complexity problem in the size of a memory and a problem of reaction speed delay occurring when a coefficient changes, may occur.
To decrease the complexity problem in the size of a memory, coefficients at predetermined angles may be used. However, since the coefficients are obtained using a transfer function approximate expression, operation performance for solving the transfer function approximate expression is required, and a time delay occurs in obtaining the coefficients. In addition, since it is difficult to solve the expression with a simple controller, the assistance of a central processing unit is required.
With the advent of DVD, digital TV and HDTV broadcasting, multi-channel audio services are now being provided. To effectively enjoy the multi-channel audio, as many loudspeakers and amplifiers as the number of channels are necessary. Accordingly, a problem that a multi-channel audio effect cannot be achieved with existing two channel output systems occurs. To solve this problem, a method for providing a similar effect to a case of using many loudspeakers, is desired when reproducing multi-channel audio over two channels.
The method can be accomplished by providing many virtual sound images in a three dimensional space using two output ports. According to a conventional method for forming virtual sound images, when forming a single virtual sound image, a set of transfer functions corresponding to the left and right ears is used. When forming N virtual sound images, N transfer functions corresponding to the right ear and N transfer functions corresponding to the left ear are used. In other words, operation complexity increases in proportion to the number of virtual sound images to be formed, and the transfer functions for virtual sound images provided at predetermined positions must be stored in a memory so that a problem that the size of the memory must be increased can occur.